(1) Field of the Invention
The invention is in the field of mine tunneling machines and methods, such as machines and methods for cutting large variable cross-section mining tunnels in hard rock.
(2) Description of the Prior Art
The most common prior art method of forming large mining tunnels in hard rock (defined as rock having a compressive strength of above 15,000 psi) is the drill-and-blast method using explosives which has many disadvantages, one of which is that it is very hazardous. Thus, there has been a long-felt need for a mobile mining machine capable of successfully cutting large mining tunnels in hard rock by mechanical means in order to replace the use of explosives. Such a machine should also be portable, that is, capable of being disassembled into components which are sufficiently small and light in weight that they may be transported in vertical mine shaft elevators.
The conventional roadheader mining machines are frequently used in horizontal mining work when the rock is soft (defined as rock having a compressive strength less than 15,000 psi), but in hard rock the cutting picks in the roadheaders are incapable of successful operation. The drill-and-blast method must then be employed.
Several prior art patents show mining machines which appear to be capable of rotating a cutterhead about a horizontal axis and swinging it across a work face about a vertical axis. Typical of these are Osterhus et al U.S. Pat. No. 2,776,824, Bergmann U.S. Pat. No. 3,307,879, Frenyo et al U.S. Pat. No. 3,929,378, Sigott et al U.S. Pat. No. 4,111,488, and Marten U.S. Pat. No. 4,230,372. All of these prior art patents disclose machines employing toothed or ripper cutter elements rather than disk cutters.
The prior art also includes Wharton U.S. Pat. No. 3,726,562 which discloses a coal mining machine having a cutterhead constructed in the shape of a shallow cone and rotatably mounted on the forward end of an elongate boom. The cutterhead, although not described in detail, appears to involve a series of picks as the cutting elements. It is not clear from the disclosure of the patent how the cutterhead is rotated and the patent disclosure does not contemplate any particular correlation between the rate of cutterhead rotation and the rate of cutterhead swing. The cutterhead is swingable both horizontally and vertically.
Stoltefuss et al U.S. Pat. No. 3,873,157 discloses a tunneling or mining machine with the cutting device rotatably mounted on the forward end of a boom which is vertically and horizontally pivotable. The cutting arrangement involves two narrow wheels or rollers carrying pick-like cutters.
Bechem U.S. Pat. No. 4,045,088 discloses a mining machine which is characterized by oscillation of a so-called drilling head about a vertical pivot axis to arcuately drive a slot cavity, the head and the rotatable disc cutters carried thereby being oscillated through a horizontal angle of about 120.degree.. Plural disc cutters are canted in a diverging manner. No cutter movement is contemplated other than horizontal oscillation.
Finally, Spurgeon U.S. Pat. No. 4,312,541 discloses a trench cutting machine comprising a main body assembly and a cutting wheel assembly. This coal mining machine moves plural rows of disk cutters horizontally about a substantially vertical axis to facilitate discharge to a conveyor. A cylinder is mounted transversely on the main body assembly and carries a pair of pistons which extend axially from each end of the cylinder. Pads are provided on each piston to bear against the side walls of the trench. Each piston has an end face within the cylinder which, together with an inner side wall of the cylinder, comprises a pressure chamber adapted to force the pads against the trench. The main body and its cylinder are free to move laterally relative to the pistons when the cylinder is pressurized. Extensible arms are provided between the pistons and the main body assembly for forcing the main body assembly and its cutting wheel forwardly to progressively cut a trench. A steering assembly is provided to shift the main body assembly laterally relative to the pistons and about the central axis of the cutting wheel.